For the thoracic vertebrae and lumbar vertebrae, a portion of the transverse processes, lamina, pedicles, and vertebral body form a structure called the spinal canal, which protects the spinal nerve. Instability in the spine, such as in the case of spondylolisthesis, can cause nerve irritation and lead to back pain, leg pain, and motor defects. Pain associated with instability in the spine is commonly treated with fusion of adjacent vertebrae. Since the early descriptions of spinal fusions in the early 20th century, advances in spine surgery techniques and devices have allowed more targeted, and less invasive approaches (Albee. 1911. Transplantation of a portion of the tibia into the spine for Pott's disease. A preliminary report. JAMA. 57:885; and Hibbs. 1912. A further consideration of an operation for Pott's disease of the spine: with report of cases from the service of the New York orthopaedic hospital. Ann. Surg. 55:682.).
Each vertebra has two laterally located structures called transverse processes. A transverse process serves as an attachment point for a number of ligaments and muscle fibers, including, for example, the longissimus muscles, multifidus muscles, rotatores muscles, and levatores costarum muscles. Transverse processes found at the thoracic vertebrae further contain articular facets that are connected to, and serve as attachment points to tubercles of ribs. Using adjacently located transverse processes to place bony material has been described previously.
Traditional lateral intertransverse process fusion, or more commonly referred to as posterolateral fusion procedures or gutter fusion, commonly involves placing bony material along two or more transverse processes of adjacently located vertebrae. There are potential benefits of fusing adjacently located transverse processes to stabilize the spine. Typically, after a period of 6 to 12 months post-surgery, patients undergoing intertransverse process fusion have higher rates of fusion than patients whose spine are secured with screws and rods alone. Such fusion process has been described to consistently have higher fusion rates compared to some other interbody fusion approaches, such as posterior lumbar interbody fusion (PLIF) (Inamdar, et al. 2006. Posterior lumbar interbody fusion versus intertransverse fusion in the treatment of lumbar spondylolisthesis. J. Ortho. Surg. 14:21). A typical problem associated with gutter fusions known in the prior art is that such techniques require new or existing (as combined with other surgical procedures) large incisions to perform, incisions which surgeons trained in newer, minimally invasive techniques typically seek to avoid. An unmet need therefore exists to develop instrumentation and tools to allow for a less invasive posterolateral gutter fusion procedure.
Traditional posterolateral fusion procedures, while generally efficacious, have several disadvantages. For instance, in traditional posterolateral fusion procedures, it is common to make a relatively large incision in the posterior region of a patient's back to access and place bony material on and/or between adjacently located transverse processes. Such typical posterolateral fusion procedures can cause great trauma to surrounding tissue and muscle, as such a procedure as known in the prior art involves creating a relatively wide incision to allow access to the transverse process for the placement of bony material. Often, access to transverse processes involves creating a relatively large incision that is approximately 6 inches (15 cm) to 12 inches (30 cm) or more. During creation of such opening to access adjacently located transverse processes, muscle fibers in the vicinity are pulled, split, and tucked. In some cases, muscle fibers are unintentionally, or unavoidably cut. There is also a possibility that blood vessels are cut during such typical posterolateral fusion procedures, leading to the undesirable consequences of interrupted blood supply, possibly slower healing, and a high level of blood loss. The vascularity of the operative area makes traditional posterolateral fusion procedures a procedure associated with a potentially high level of complications (Truchly and Thompson. 1962. Posterolateral Fusion of the Lumbosacral Spine. J Bone and Joint Surg. 44-A:505). In some cases, there is a risk of injury to nerves with such large incisions, resulting in nerve damage, decreased sensation during and after surgery, and high levels of post-surgical pain.
In typical posterolateral fusion procedures, once bony material is laid between transverse processes, there is difficulty in keeping bony material in the correct place. Due to the large incision to access the transverse processes, during healing, such bony material may shift or move to other unintended areas. Further, bony material may be placed further anterior, beyond the transverse processes due to, for example, surgeon error and suboptimal surgical technique and instrumentation.